Add sub issue list support (#32940)

Just like GitHub, show issue icon/title when the issue number is in a list

routers/init.go

@@ -133,7 +133,7 @@ func InitWebInstalled(ctx context.Context) {
 
 	highlight.NewContext()
 	external.RegisterRenderers()
-	markup.Init(markup_service.ProcessorHelper())
+	markup.Init(markup_service.FormalRenderHelperFuncs())
 
 	if setting.EnableSQLite3 {
 		log.Info("SQLite3 support is enabled")